When monitoring or measuring signals, waveforms that represent the signals are typically compared to a standard, or specification limit, to establish whether or not the signals comply with the standard. For example, An eye diagram, which represents the waveform of a multi-valued signal, is compared to a mask that is defined by a standard. By superimposing the mask on the eye diagram it can be determined whether or not features of the waveform, such as one and zero levels, crossing time, and crossing level violate the mask and fail to comply with the standard. A mask violation occurs when any portion of the eye diagram falls either on, or within, the perimeter of the mask. Compliance with a designated standard is indicated by an absence of mask violations, whereas non-compliance with the standard is indicated by one or more mask violations. However, when monitoring or measuring signals there is a need to determine not only whether or not a waveform complies with a standard, but to determine also by what margin the waveform complies or fails to comply with that standard.
An apparatus and method constructed according to the preferred embodiments of the present invention determine the compliance margin of a waveform relative to a standard. The compliance margin indicates the extent to which the waveform either complies or fails to comply with the standard. The apparatus constructed according to the first preferred embodiment of the present invention includes an acquisition system that captures the waveform of an applied signal in a display space, and a memory that stores a representation of a series of scaled masks in the display space. Each scaled mask in the series is a version of the standard that is scaled relative to the standard according to a corresponding scale factor. A comparator determines which scaled masks in the series coincide with the waveform at one or more predesignated locations in the display space by comparing the wave to the represented series of scaled masks at the one or more locations. An output device indicates the compliance margin of the waveform based on the corresponding scale factors of the scaled masks that coincide with the waveform at the one or more locations in the display space.
The method constructed according to the second preferred embodiment of the present invention includes representing a series of scaled masks in the display space of a waveform wherein each scaled mask is a version of the standard that is scaled relative to the standard according to a corresponding scale factor. At one or more predesignated locations in the display space, the waveform is compared to the represented series of scaled masks to determine which of the scaled masks coincides with the waveform at the one or more locations. The compliance margin of the waveform is designated based on the corresponding scale factors of the scaled masks that coincide with the waveform at the one or more locations in the display space.